Transmission of pictures



March 15, 1932.

R. D. KELL TRANSMISSION OF PICTURES Filed Nov. 16, 1929 Ill Fig.4.

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' eliminated from the Patented Mar. 15, 1932 RAY D. KELL, OF SCOTIA,

NEW YORK, ASSIGNOR T GENERAL ELEOTRIG COMPANY,.A

CORPORATION OF NEW YORK TRANSMISSION OF PIOTURES Application filed November 16, 1929. Serial No. 407,762.

My invention relates to the transmission of pictures, and has for its principal object the provision of an improved apparatus and method of, operation whereby synchronism :s' is readily maintained between the moving parts of the picture transmitting and receiving apparatus.

In the past various types of apparatus have been provided wherein electrical impulses or signals modulated in accordance with the shade of the successive elemental areas have been utilized for transmitting pic-' .tures either between radio transmitters and receivers or between transmitters and receiversinterconnected by electrical conductors.

In the operation of such apparatus it is usually essential that the movable parts of the transmitter and receiver be operated in synchronism with one another. This result has been achieved in various ways which have not been altogether satisfactory for the reason that exact synchronism is not maintained and the picture is more or less distorted.

It is known that a television or picturetransmitting signal consists of a complex wave containing frequencies distributed between the picture frequency and the frequency produced by the maximum resolving power of the scanning elements such, for example,.as twenty cycles for twenty pictures per second, and twenty-three thousand cycles for twenty threepicture elements. Due to the fact that the picture is composed of such a wide band of frequencies, a small part of the frequencies may be eliminated from the transmitted signal without a perceptible change in the quality of the picture. In accordance with my invention a narrow band (about one percent) of the frequencies is transmitted signal, and

a synchronizing frequency is introduced into the gap thus produced. This synchronizing frequency may be supplied from any suitable source such as an alternator driven by' the same motor that moves the scanning eleparatuswherein light from 'ning disc 13. Under ment. At the receiver the signals containingthe picture and synchronizing frequencies are passed through suitable filters so that the pic- I ture frequencies are utilized to build up the picture while the synchronizing frequency is utilized to maintain synchronism between the movable parts of the transmitter and receiver.

My invention will be better understood from the following description when considered in connection with the accompanying drawings, andits scope will be pointed out in the appended claims. I Referring to'the drawings, Figs. 1 and 2 show picture transmitting and. receiving apparatus wherein my inventionhas been embodied, and Figs. 3 to 6 are explanatory diagrams relating to the operation of the apparatus.

Fig. 1 illustrates a picture-transmitting apa suitable source 10 is applied to a picture 11 through a lens 12, a scanning disc 13, and a lens 14. Light reflected from the successive elemental areas of the picture tive cell 15, which is connected to the input circuit of an amplifier 16 in a well known manner. The output circuit of the amplifier 16 is connected to a radio transmitter 17 through a filter 18 which functions to eliminate a narrow band of frequencies corresponding to the selected synchronizing frequency. The radio transmitter 17 is also connected to an alternator 19 mounted'on the shaft of a motor 20, which drives the scanthese conditions potential of synchronizing and, together with the picture signal frequencies, is transmitted to the receivlng apparatus. As is well known, the scanning .disc 13 is provided with a plurality of spifrequency is applied to the input circuit of the radio transmitter 17 11 is recelved by a light sensiis connected-to a neon lamp 22 or the like through an amplifier'23. Theradio receiver 21 is also connected to an alternating current motor 24 which is coupled to a scanning disc 26 interposed betweenthe modulated light source 22 and the receiving screen 27. The connections between the receiver 21 and the motor 24 include a pair of electric discharge and 31. v The device 29 is provided with an input circuit, whlch includes a resistor 32 and a reactor 33, and with an output circuit. which ncludes a reactor 34, a capacitor connected in shunt to the reactor 34, and a suitable plate current source 36. Also connected to the output circuit of the device 29 is a capacitor 37 and the primary winding of the transformer 31. The input circuit of the device 28 is connected to a bias potential source 38 through the secondary circuit of the transformer 31, and the output circuit of this device is connected to the motor 24 through a plate battery 29 and the transformer 30.

The picture and synchronizing. signals are applied to the resistor 32, which controls the potential of the input circuit of the device 29. 'The inductances. 33 and 34 are coupled together, and the reactor 34 and. the capacitor 35 are so designed as to form -a circuit which is resonant to the synchronizing frequency. Asis well understood. the resistance in the tuned circuit formed by the reactor 34 and the capacitor 35 limits the selectivity of the tuned circuit. The coupling between the reactors 33 and 34 is so adjusted that the effective resistance of the resonant circuit approaches zero at resonance, thus increasing the selectivity of the circuit and at the same time amplifying the synchronizing signal in the device 29, from which it is supplied to the amplifying device 28 and to themotor 24.

It has been found that the synchronizing frequency may be mixed with the picture di-' rectly. at the transmitter, the synchronizing frequency current is amplified sufliciently to frequency being of such small amplitude that it is not noticeable on the receiving screen. By means of the devices 28 and 29 and their interconnecting circuits the synchronizing drive the disc 26 in synchronism with the disc 13 by means of the motor 24. With the de-. scribed circuit it has beenfound possible toselect a 600-cycle frequency from the picture signal. mixed with a'GOO-cycle synchronizing frequency the magnitude of the synchronizing frequency to the picture frequencies being of the order of 1 to 100 as received.

The result obtained is indicated by Figs. 3,4, 5,and 6, wherein the curve of Fig. 3 represents thepicture signal, Fig. 4 represents the picture signal with a gap produced by the filter 18, Fig. 5 represents the combined picture and synchronizing signals, and Fig. 6 represents the synchronizing signal.

What I claim as new and desire tosecure by Letters Patent of the United States is:

1. The method of maintaining synchros nism between picture-transmitting and receiving apparatus which includes producing a frequency gap in the picture signal, and

introducing a synchronizing signal in saiddevices 28 and 29 and a pair of transformers g P I a 2. The method of obtaining synchronism between picture-transmitting and receiving.

nal having a frequency lying in said portion with the remainder of said picture signal.

4. The combination of means including a movable element for scanning a icture, means for producing picture signals ependent on the shade of the picture, means for eliminating a predetermined intermediate band of frequencies of said signal, means operable in accordance with the motion of said movable member for combining a synchronizing signal having a frequency lying in said band with the remainder of said picture .signal, and a picture-receiving apparatus including means for separating said picture and synchronizing, signals, a light source modulated in accordance with said picture signal, a movable scanning member, and means arranged to cause said scanning memher to be moved in accordance with said synchronizing signal.

5. In picture transmission wherein a relatively wide'band of frequencies are. transmitted, the method which comprises f'producw mg a frequency gap in said band, introducing in said gap a synchronizing. frequency and modulating a carrier the resulting frequencies.

6. In picture transmission wherein a relaroducing a rent varied in accordance with said scanningray as modified by said object, said current including a wide band of frequencies, means for suppressing one of the frequencies of said band, a-source of alternating current having a frequency within said band, a carrier current, means for modulatin said carrier current by the unsuppressed requencies of said band, and-means for modulatmg said carrier current by the output of said source.

In witnesszwhereof, I have hereunto set my hand this 15thday ofNovember', .1929.

RAY'D. KELL. 

